I connected a 16GB SDHD Class 4 card to my PC with a dongle reader. A class 4 card is supposed to support a minimum of 4 MB/s sustained speed. I grabbed a couple of large, 4.4 GB each, files and copied them to the SD card with Nautilus. The transfer rate started out at 60 MB/s and rapidly dropped to 50 then 40 and slowly dropped to 3.5 MB/s after about 3 GB transferred and it is still dropping.

The PC will copy from drive to drive at 65 MB/s so I do not think the issue is reading from the hard drive.

I am confused about the transfer speeds which Nautilus is showing. Obviously I am not really transferring to this card at 50+ MB/s. If I was moving data from hard drive to cache I would expect much more speed - I have 8 GB of RAM on the PC.

That said, I have stopped the transfer and attempted to unmount the card. I get the message "Failed to eject media; one or more volumes on the media are busy." This has been going on for several minutes so some activity is going on in the background.

Can someone enlighten me as to what is actually taking place?

TIA,

Ken

To improve life span writes to SD cards are usually cached to memory first, then written in large chunks to the card to reduce wear.

The initial fast speed is because its being done in memory, then as the writes start to happen and the cache is filled it slows to actual write speeds.

After the copy is finished (or stopped) the cache still has to be written which can take minutes to complete.

As nautillus is multi-tasking the copy/write process is still running in the background when you click the unmount.

Thanks JonathanWilson,

I understand that Nautilus works in the background. I have some external HDDs which connect via USB. When I unmount them I see a dialog that Nautilus is completing writes to the drive.

As to my poor SD card... I put it back in the built in SD card reader in my netbook - what I had originally purchased it for - and tried slamming a DVD size file (nominal 4.4 GB or so) to it. It wrote at about 9 GB/s until it hit the 4 GB limit for a FAT 32 file system So I formatted the card for ext2 then I got some errors about could not mount - even though it seemed to mount. So I went back with fdisk, created a Linux partition, created an ext2 file system and tried again. The file copied from the SSD on the netbook to the SD card at a consistent 9.1 MB/s.

Now why am I doing this Oh yes! I plan to put a couple of DVD size gpg files on the SD card to store data securely in the event I take the netbook on the road. Looks like I am good to go with that part.

As to the strange performance of the USB dongle reader thing... I think it is probably not SDHC compatible. Back when I purchased it a 1 GB SD drive was BIG. I will try it again and if I get similar results I may drop $8 at Wally World and get one which is labled for SDHC - or just copy the files across the network.

Ken

The built in reader in the desktop had a bad cable - got that replaced and it works fine. Transfer speeds as expected.

Ken